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Re: [Discuss-gnuradio] Question regarding the DBSRX frequency range and
Re: [Discuss-gnuradio] Question regarding the DBSRX frequency range and bandwidth
Wed, 27 Jun 2007 21:36:51 +0200
2007/6/27, Matt Ettus <address@hidden>:
Trond Danielsen wrote:
> I have a small question regarding the frequency range and bandwidth of
> the DBSRX daughterboard from www.ettus.com. According to the
> daughterboard datasheet  the frequency range is from 800 to 2400
> MHz, and the adjustable bandwidth is from 1 to 60 MHz. However, the
> datasheet for the MAX2118  states a frequency range from 925 to
> 2175 MHz, and the adjustable LP filter BW is 4 to 33 MHz.
> If someone could provide some information that would enlighten me on
> these matters I would be most grateful.
The MAX2118 datasheet says that it covers 925 to 2175 MHz. They
spec that because it is the range that their typical customer needs (for
small satellite dish IFs). However, I have never found one which
doesn't work to the larger 800 MHz to 2400 MHz range. Maxim guarantees
925 to 2175, I guarantee the larger range.
When Maxim states that their maximum LPF bandwidth is 33 MHz, they
mean one-sided bandwidth (i.e. 0 to 33 MHz). Since it is used in a
direct conversion IQ system, that actually gives a 66 MHz bandwidth (-33
MHz to +33 MHz). Since that is beyond nyquist for our ADC, I spec to 60
MHz (+/- 30 MHz).
On the low end, they specify 4 MHz, which is really 8 MHz (+/-4 MHz)
of RF bandwidth. The filter is actually capable of going to a much
narrow frequency, but it is outside of Maxim's specs, since nobody in
the small satellite dish market cares about less than 8 MHz of BW. So I
spec that it goes down to 1 MHz wide. It should be noted that when you
go below 4 MHz wide (2 MHz in Maxim-speak) that your noise floor will
rise a bit and phase noise may also rise.
Thank you very much for the clarification! I will add this information
to the wiki, just in case anyone else wonders about the same.